A radio transmission apparatus radiates radio frequency (RF) electromagnetic energy in a radiation pattern. The radio transmission apparatus typically has at least one antenna element that is used to control the characteristics of the radiation pattern such as its shape at one or more particular RF frequencies.
The radiation pattern is dependent upon the RF electric currents in the radio transmission apparatus. RF electric currents are driven in the antenna element and may also exist in other conductive elements within the radio transmission apparatus such as a ground plane.
It is often desirable to control the shape of a radiation pattern so that the radio transmission apparatus radiates more strongly in a first direction than a second direction. This control improves the efficiency of the radio transmission apparatus in the first direction at the expense of efficiency in the second direction.
It would be desirable to control electric currents that exist within a conductive element, particularly a ground plane, and thereby control the radiation pattern of the radio transmission apparatus.